Conventional automobile seats generally include spring members attached to a seat frame, a pad material such as a foamed material or cotton placed thereon, and a skin such as a vinyl leather, woven cloth, or leather covered thereon.
On the other hand, seats other than the automobile seats generally include a pad material placed on the frame and covered with a skin, and some of them also include spring members for enhancing the cushioning characteristics.
However, such seats are mostly thick, heavy and costly.
In view of the above, a variety of lightweight, inexpensive and thin seats have been recently proposed, and the inventors of this application have developed thin seats having a lightweight net of a three-dimensional structure that is provided with desired characteristics (spring characteristics, damping characteristics and the like) sufficient for a cushioning material.
A three-dimensional net (hereinafter referred to as 3-D net) employed in such thin seats is formed of a three-dimensional knit fabric, which has a ground fabric formed into, for example, a knit texture or a honeycomb-shaped (hexagonal) mesh. The 3-D net has a three-layered solid truss structure in which an upper mesh layer and a lower mesh layer are connected to each other by a pile layer having a large number of piles. Each yarn of the upper mesh layer and the lower mesh layer is formed by twisting a number of fine threads, while each of the piles is formed of a single thick string to provide the three-dimensional knit fabric with rigidity.
FIG. 7 depicts an example of the above-described conventional thin seats, which is built for two persons and includes a seat cushion 50 having a 3-D net and a seat back 52 extending upwards from a rear edge of the seat cushion 50.
As shown in FIG. 7 and FIGS. 8A and 8B, the seat cushion 50 includes a seat cushion frame 54 and a 3-D net 56 stretched over the seat cushion frame 54. An outer edge portion of the 3-D net 56 is sewn to an inner edge portion of a trim material (skin) 58 and that of a tension member 60, while an outer edge portion of the trim material 58 and that of the tension member 60 are wound around the seat cushion frame 54 and then engaged with a trim retainer 64 by a retainer piece 62, thereby applying a predetermined tension to the seat cushion 50.
However, when a person sits on the conventional thin seat of the above-described construction, a tension is applied to the trim material 58 and increases the tension of the seat cushion 50, resulting in an increase in side pressure. Accordingly, when a person sits on a portion offset from the center of the seat cushion 50 or two persons sit on the seat cushion 50, his or their postures tend to incline to some extent, deteriorating the sitting feeling.
The present invention has been developed to overcome the above-described disadvantages inherent in the prior art and is intended to provide a thin seat having improved cushioning characteristics that enables a seat occupant to have a good posture and can withstand a long-term use.